Apparatus and method for measuring subject work rate on an exercise device

ABSTRACT

Method and apparatus for accurately simulating locomotion in a weightless environment, specifically to prevent atrophy of a subject&#39;s musculoskeletal and cardiorespiratory systems during space travel, are disclosed. Forces, including the vertical, horizontal and lateral force generated by an individual during locomotion on a treadmill, utilizing a rigid belt with rigid transfer elements supported by low friction bogies are measured by strain gauges sensitive in their respective direction. The vertical forces produced by securing the subject to the treadmill via bungee cords in conjunction with the measured velocity of the treadmill, and the mode of locomotion are used to determine the subject&#39;s equivalent weight. The other horizontal and lateral forces are used to determine the external work produced by the subject when locomotion is performed on a nonlevel surface with an effective grade angle. The measured forces are related in such a way that the grade angle is easily determined. A motor and additional circuitry can be added to the apparatus to measure and force a subject to maintain a predetermined work rate associated with a preselected grade angle and tread velocity.

ORIGIN OF THE INVENTION

The invention described herein was made by an employee of the UnitedStates Government and may be manufactured and used by and for theGovernment of the United States of America for governmental purposeswithout payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to an apparatus and method associated withexercise equipment, and particularly a treadmill, in a substantiallyweightless environment, such as exists in space flight activity.

2. Description of the Prior Art

Although an orbiting spacecraft or a spacecraft in free-fall is stillobviously within the ambit of gravitational forces exerted by planets orother heavenly bodies, the gravitational exertion on the spacecraft andliving beings within is balanced by centrifugal or other accelerativeforces. This state is hereinafter called weightlessness. Such a statereduces many physical loads on living beings and absolutely precludesnormal human locomotion.

The human body adapts to a wide range of environmental conditions.Researchers have proven that reduced locomotor activity reduces thecardiorespiratory capacity, muscle strength, mass and endurance, bloodvolume, and bone mineral concentration and strength. Thus, in anunstressed environment such as weightlessness, bone and muscle undergorapid atrophy and cardio-respiratory capacity will be reduced such thatafter several months crewmen will no longer be able to walk on Earth.

Persons or other living beings must exercise in weightlessness as onEarth to maintain their cardiovascular, musculoskeletal, and othersystems for normal activity on Earth. Human locomotion is an especiallyimportant exercise under these conditions. Primary concerns of suchexercise are the foot ground forces and work level. These are absolutelydependent upon body weight, speed, grade and mode (walking or running).Since weight is a constant factor on Earth, locomotor forces and worklevel are not usually measured, instead they are indirectly determinedby speed and grade. Body weight and grade are provided by gravitationalforces which are nulled in space flight hence treadmills designed forEarth are unusable there.

Currently, the only exerciser capable of providing locomotor activity ina weightless environment of a spacecraft is a treadmill with provisionsfor providing an axial truncal force on an individual to simulate thebody weight of the individual. Previous designs are only partiallyeffective since actual forces and other stresses on the body are notbeing measured, are unknown and hence cannot be documented nor used tocontrol the exercise. Also, means are not available to controlequivalent grades.

A treadmill device that has been employed by the Union of SovietSocialist Republics on space ventures sponsored by that country hasemployed elastic bungees and a harness to provide an adjustable, partlyequivalent body weight or foot ground force against the tread. It is notbelieved that any such device includes a way of measuring thatequivalent weight force. It is further believed that with such a devicethere is no elevation or grade provision or means for measuring orcontrolling grade. It is unknown but assumed that speed is measured andcontrolled.

Treadmill devices that have been employed by the United States on itsspace ventures provide mechanical means for applying forces estimated tobe equivalent to body weight. These devices also have speed indicatorsfor measuring the speed of the belt but heretofore, there has been noway to provide for and/or measure an equivalent grade. Without suchinformation, neither forces nor work can be measured or controlled.

In addition, only passive treadmills have been used to date in theUnited States program and these require some minimum equivalent gradetypically 10%, and this also limits their utility.

Therefore, it is a feature of this invention to provide a method ofaccurately simulating Earth locomotion in a weightless environment bymeasurement and control of essential parameters.

It is another feature of this invention to provide a small, lightweightapparatus for simulating locomotion in a weightless environment.

It is another feature of this invention to provide a method of measuringforces exerted on a body during locomotion.

It is another feature of this invention to provide an apparatus formeasuring forces exerted on a body during locomotion.

It is another feature of this invention to provide a method formeasuring and controlling the vertical foot ground force.

It is another feature of this invention to provide an apparatus formeasuring and controlling the vertical foot ground force.

It is another feature of this invention to provide a method forproducing, measuring, and controlling the equivalent grade.

It is another feature of this invention to provide an apparatus forproducing, measuring and controlling the equivalent grade.

It is yet another feature of this invention to provide a means fordetermining locomotor mode by visual inspection.

It is yet another feature of this invention to provide improved methodand apparatus for generating a requisite work rate by an individualduring locomotion.

It is yet another feature of this invention to provide an improvedapparatus of correlating the actual measured forces to known work ratelevel measurement units such as body weight and grade of the surface.

SUMMARY OF THE INVENTION

The inventive apparatus described herein for use in a weightlessenvironment comprises in its preferred embodiments a treadmill having atransversely rigid, longitudinally flexible, continuous tread on whichthe user is positioned and pressed downward toward the surface of thetread. The downward force is generated by, for example, an adjustableharness or other suitable mechanical means that transmits force fromcables fore and aft of the subject and including a meter or otherappropriate indicator of static or mean equivalent body weight.Adjustments are made until the downward force equals the desiredequivalent weight. A first plurality or series of strain elements,sensitive only in the vertical direction, for example vertical straingauges, (normal to the plane of the tread), while being insensitive tohorizontal forces, are connected at appropriately spaced positions onthe treadmill. Preferably, the vertical strain gauges are mountedbetween the tread support members supporting the area of the treadcarrying the subject and the vertical force sustaining structure of thetreadmill, exerting downward pressure on respective ones of the matchedpair. The electrical output of each vertical strain gauge is connectedto a summation and averaging network to produce an equivalent bodyweight measure. The registered instantaneous measurement of verticalforce is indicative of the mode of locomotion and also has researchvalue in its own right. Average values during locomotion are used indetermination of the subject work rate, grade, and equivalent bodyweight.

The speed of movement of the belt is measured by means of a tachometeror the like in conventional fashion. The mean weight measure inconjunction with the speed is used to determine the subject Earthequivalent work rate, which is also the total work rate when there is noequivalent grade of the belt.

When locomotion occurs on a surface with an equivalent grade of greaterthan zero, in addition to measuring the vertical forces, horizontalforces are also first developed and then measured. To effect anequivalent grade, forces may be applied by adjusting tension in thecables going forward from the user at a different value than those goingrearward from the user, or vice versa. On the other hand, with balancedor equal forces the subject, by leaning forward, automatically generatesa horizontal vector (when cables are connected for and aft of thesubject) that also creates an equivalent grade. Measuring the differencein the two horizontal fore and aft vector values is accomplished byconnecting a second series of a matched set of horizontal strain gaugesto the forward cable(s) and to the rearward cable(s), respectively, withrespect to the position of the exerciser. A horizontal strain gauge issensitive to the horizontal force applied, but is insensitive to avertical force. By adjusting circuitry to subtract any differences inthe gauges, the net horizontal force is obtained. By treating therespective vertical and horizontal forces as orthogonal values, it isalso possible to develop a value for the grade and continuous meansubject weight.

The net horizontal force times the speed is equivalent to external workrate, usually expressed in terms of grade and speed. Total work forceperformed by a subject consists of the internal work determined bysubject weight, speed, and mode, plus the external work determined bygrade, speed and subject weight.

If handles are provided so that the user can effectively apply pressureto them as well as to the treadmill belt or other surface, similarvertical and horizontal strain gauges are included connected to thesehandles. The handle values are added to the treadmill foot force valuespreviously discussed to obtain the total work rate values.

By the addition of a servo-controlled motor, desired equivalent grade ofany range including zero (level) and negative (downhill) may beachieved.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features, advantages andobjects of the invention, as well as others which will become apparent,are attained and can be understood in detail, more particulardescription of the invention briefly summarized above may be had byreference to the exemplary preferred embodiments thereof which areillustrated in the drawings, which form a part of this specification. Itis to be noted, however, that the appended drawings illustrate onlytypical preferred embodiments of the invention and are not to beconsidered limiting of its scope as the invention may admit to otherequally effective embodiments.

FIG. 1a is the conventional reference system used here for vectorcomponents of a human subject's foot ground force during locomotion.

FIG. 1b shows examples of typical vector components of subject footground force during a walk and fast run on level ground on Earth.

FIG. 2a is a front view of an apparatus used to simulate body weight ina weightless environment.

FIG. 2b is a side view of the apparatus shown in FIG. 2a.

FIG. 3a is a representation of the force vectors associated with forcesgenerated by foot to ground contact during locomotion on a level surfaceand the balance forces generated by balanced bungee cords attached to asubject.

FIG. 3b is a representation of the force vectors associated with forcesgenerated by foot ground force contact during locomotion and theunbalanced forces generated by the bungee cords attached a subject.

FIG. 4a is a representation of a physical configuration of verticalstrain gauges and a segmented belt with rigid transfer elementssupported by low friction bogies in accordance with a preferredembodiment of this invention.

FIG. 4b is a cross sectional view of one of the rigid transfer elementssupported by low friction bogies shown in FIG. 4a.

FIG. 5a is a simplified schematic diagram representation of anelectrical configuration of the vertical strain gauges to generate asignal proportional to the total vertical forces measured.

FIG. 5b is a simplified schematic diagram representation of an alternatescheme for summation of the total vertical forces measured by thevertical strain gauges.

FIG. 5c is a simplified schematic diagram representation of theaveraging circuitry used to average the vertical forces measured by thevertical strain gauges.

FIG. 6 is a diagram of an apparatus used to measure the forces exertedon a treadmill by a subject in accordance with a preferred embodiment ofthis invention.

FIG. 7a is a vector representation of the forces on the body of asubject during locomotion on a level surface, at grade angle zero.

FIG. 7b is a vector representation of the forces on the body of asubject during locomotion on a level surface, surface in a gravityfield.

FIG. 7c is a vector representation of the forces on the body of asubject during locomotion on a surface with an equivalent grade angle θ.

FIG. 8a is a simplified schematic diagram representation of asubtracting network used to find a net horizontal force.

FIG. 8b is a simplified schematic diagram representation of an alternatescheme used to generate a net horizontal force.

FIG. 8c is a simplified schematic diagram representation of summingamplifiers used to generate a net horizontal force.

FIG. 9a is a diagram of an apparatus used to measure component forcesattributed to the subjects use of a handle during locomotion on atreadmill.

FIG. 9b is a side view of the apparatus shown in FIG. 9a.

FIG. 10 is a flow diagram of a method used to generate a desired workrate on a motor controlled treadmill.

FIG. 11 is a representation of an apparatus which provides means formeasuring and maintaining a predetermined equivalent grade and for workrate applied to a motor controlled treadmill by a user.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Locomotion on Earth requires expenditure of metabolic energy or work andgeneration of large foot ground forces. The first of these determinescardiorespiratory capacity or condition while the latter determines boneand muscle status. Except for limited research foot ground force hasreceived little attention on Earth but in space flight both work andfoot ground force are crucial.

Hereinafter, "subject" refers to the treadmill user and the two termsare used interchangeably.

Subject foot ground force and work achieved during locomotion on Earthare absolutely dependent on four factors:

subject body weight;

subject speed;

surface grade or incline, 1/4; and

subject locomotor mode, walk or run.

In weightlessness, body weight and surface grade quantities become Earthequivalents and will be used interchangeably. In identifying thesequalities, the foot ground force generated by an individual must bedetermined. Now referring to the figures and first to FIG. 1a, aconventional reference system is used to identify vector forcecomponents of a subject's foot to ground force during locomotion.

FIG. 1b shows examples of typical instantaneous vertical F_(z),horizontal F_(x), and lateral F_(y) vector components of subject footground force during a walk 90 and a fast run 91 on level ground onEarth. During walking, vertical forces between 1 and 1.35 times bodyweight are generated. During running, the vertical forces generatedrange from between 2 and 3 or more times body weight. These are forcesfrom a single step. During walking there is an overlap of forces. Whilerunning, each foot is clear of all support for a portion of each stepand all forces go to zero.

In FIG. 1a, the major locomotor foot ground force component is verticalforce F_(z), and net horizontal forces during unaccelerated locomotionat zero grade are zero over a stride (right and left step) cycle.Maximum F_(z) vertical force varies directly with body weight andvelocity during locomotion. It increases abruptly with a transition fromwalk to run and continues to increase but more slowly with velocity inthe run mode. Treadmills with capacity for measurement of foot groundforce are extremely rare.

Once foot to ground force measurements are made, work performed by anindividual, hereinafter called subject work, can be determined. Subjectwork is defined as the sum of internal work, such as occurs on levelground, plus external work which is zero except at some grade. Internalwork is complex and not measured, but empirically estimated from speedand subject weight. External work is a simple function of grade andvelocity.

On Earth, treadmills are normally equipped with speed and gradeindications and imposed subject work is normally expressed in only thoseterms. For the researcher who requires an absolute measure of externalwork, subject weight is a readily available property of each individual.Mode may be directly observed.

In a weightlessness condition, it is obvious that an incline, or changein grade, of the tread of a treadmill, or the particular body weight ofthe user, will have no effect on the forces at play or the level of workbeing performed. Accordingly, references to this invention with respectto grade, grade measurement, grade control, etc., refer to simulatedEarth-equivalent incline. Similarly, references to this invention hereinwith respect to body weight forces refer to simulated Earth-equivalentbody weight forces, or body weight forces as measured on Earth.

In weightlessness, weight equivalent force and grades must be generatedand controlled and speed should be known and controlled. Usually, thetreadmill in space will not be under the observation of the investigatoror flight surgeon and mode must be obtained from data. At this point intime, researchers are also very interested in foot ground force inweightlessness, especially the net vertical force F_(z).

Such forces are of particular interest since leg and back muscle massand strength are determined by force level in locomotor exercise. Thefeatures necessary to measure and control these factors are implementedas follows.

FORCE MEASUREMENT AND CONTROL

Fundamental to all locomotor processes in space is application of aconstant longitudinal force to the subject force normally equivalent tosubject body weight on Earth. This has been accomplished to date in theUnited States and Union of Soviet Socialist Republics flight treadmillsby elastic bungee cords and harness arrangements. The United Statesharness arrangement is shown in FIGS. 2a and 2b. Elastic bungees 150 areconnected to a hip and shoulder harness 151 and 152 respectively. Thesebungees 150 are connected fore and aft as shown in FIG. 2b, laterally asdone in the Union of Soviet Socialist Republics, or in any otheracceptable manner and in each case the arrangement produces a singleforce vector 153 coincident with the subject's longitudinal axisequivalent in direction to body weight force vector on Earth.

The vector diagram in FIG. 3a shows the resultant force and static footground force on a subject 164 on level ground. Tension and angle incables 160 and 161 are adjusted such that the vectors X₁ and X₂ areequal and balanced in the horizontal direction and vector Z₁ and Z₂ arecombined to produce a single vertical force, F_(z), normal to the tread.FIG. 3b shows the vector diagram of the resultant forces generated on atreadmill with equivalent grade of greater than zero. This figure willbe explained in greater detail further on in the application. Currently,only estimates of this force are available from bungees' adjustments ormechanical settings.

Referring now to FIG. 4a and 4b, an apparatus for accurately measuring asubject's static equivalent body weight is shown. A subject's force issupported by a segmented tread, generally referred to as 183, consistingof rigid transverse elements 184 connected to each other such that theycan flex in the longitudinal axis. Each segment is supported to its endsby a low friction bogey or bearing 188 running in oval tracks 187. Thesetracks 187 are mechanically isolated except for support of strainsensitive elements 185 and 186 supported by rigid structure 189, whichalso carries the subject body weight force mechanism. Strain elements185 and 186 are sensitive only in the vertical axis to eliminate errorsand noise from undesired forces. Foot ground forces normal to the treadare transmitted through the bogies 188 to the support rails 187 andproduce electrical signals in the force sensitive elements 185 and 186.This is only one possible embodiment.

The more common belt tread, supported by either a platen or multiplerollers, could be instrumented by placing similar strain elementsbetween isolated platen or roller support and structure. A variety offorce sensitive transducers are available and could be used. The onesselected for use here are the well known bridge connected strain gauges.Since several support points are required, the gauges must be of equalsensitivity and their outputs summed to measure total force.

The total vertical force F_(z) is determined from the individual straingauge signals, as represented by boxes 185 and 186 in FIG. 4a. Severaldifferent circuit configurations may be used to achieve this result. Forexample, in FIG. 5a, the strain gauges 191, 192, 193, and 194 areavailable in matched sets such that they can be used in parallelalignment to provide the total force. Terminals A and B are labeled toshow the appropriate orientation of the strain gauges. This is theconfiguration used in the preferred embodiment of this invention. Avariable offset current or voltage may be used to cancel weight and toeliminate any zero drift via the variable resistance network 195 and196. An alternate scheme for summation of the total vertical forcemeasured from the strain gauges is shown in FIG. 5b. The outputs of thestrain gauges 191, 192, 193, and 194 are fed into their respectiveoperational amplifiers, and then into a summing network includingresistance networks 195, 196, 197, and 198 and gain corrector 200 toproduce an instantaneous vertical force value F_(z).

Output of this ensemble is now a measure of static equivalent bodyweight and may be suitably scaled and at zero grade to body weightpresented on a digital volt meter in pounds or other quantity.

By suitable design of treadmill structure, the force elements cangenerate instantaneous vertical force F_(z) that occur as in FIG. 1bduring locomotion and these may be recorded for study.

FIG. 6 shows an example of such a design. Tread means 204 is supportedby tread support means 205 to which vertical strain elements 206 and 207are attached. Assuming element 206 measures one vertical force F_(Z1)and element 207 measures another F_(Z2), the total instantaneousvertical force F_(Z) is generated by an adding network 208 and thenrecorded on a recorder 209.

Subsequently, this total vertical force is averaged 210 over time toproduce an average dynamic vertical force on the subject by the typicalaveraging circuit shown in FIG. 5c. (Hereinafter mean and average willbe used interchangeably.) In combination with operational amplifier 203,the values of the components resistor 201 and capacitor 202 will varywith the operational requirements chosen and can be easily determined byone skilled in the art. More complex designs may be required dependingon allowable error. This average vertical force can also be used todetermine the equivalent body weight measure and display it. As will beshown later, this mean force vector is required in measurement of andcontrol of equivalent grades. Instantaneous vertical force is also anindicator of locomotor mode and this may be automatically detected bysuitable circuitry or by inspection.

There are two methods for development of a mean vertical force F_(Z)signal for later use. Value of body weight can be assumed to remainconstant, that is the subject weight equivalent force generators areconstant and stable and small geometric errors during grade variationare negligible and a fixed, stored value obtained during body weightadjustment is used. A more accurate method is to measure the mean of thedynamic vertical force generated during locomotion, which must be equalto equivalent body weight, and this may be done as above with standardcircuitry or with more complex frequency selective circuits.

MEASUREMENT AND CONTROL OF GRADE

In weightlessness, the resultant vector force of the sum of thecomponent vector forces becomes equivalent to that of weight on Earth.This is illustrated in FIGS. 7a, 7b, and 7c. FIG. 7a illustrates theresultant force vector on a subject that is on a level treadmill. Thestatic foot ground force is equal to the vertical force F_(Z) and alsosubject body weight, shown as F_(Z) = F_(BW). In weightlessness, ifbalanced force vectors of correct magnitude are applied as in FIG. 3a,then the resultant static foot ground force is also equal to the F_(BW)on Earth. If the treadmill on Earth is elevated by an angle θ as in asin FIG. 7b, then F_(BW) is split into components F_(Z') and F_(X').F_(X), F_(Y), and F_(Z) refer to the subject reference system andF_(X'), F_(Y'), and F_(Z') refer to a treadmill reference system inwhich positive F_(Z') is a vector coincident with and normal to thetread's long axis facing forward, positive F_(Y') is parallel to thetread's transverse, left directed axis and positive F_(X') is the axisnormal to the tread and directed toward it.

In weightlessness, there is no reference weight vector. However, theangle between the resultant vector of F_(BW) and F_(Z') in FIGS. 7b and7c is equivalent to the elevation angle. On Earth, a vector componentF_(X') is generated at any angle above zero. On a treadmill inweightlessness, this vector may be generated by resistance or friction,which is always present in a passive or subject driven treadmill. Hencesuch a treadmill must always operate at some equivalent grade. Ifsubject weight on Earth and equivalent weight in space are equal, thepassive treadmill will have to be elevated to the same angle, θ, onEarth. Thus, to know and control the grade angle, it must be measured.The basis of such measurement follows.

To develop a force along the tread, horizontal force F_(X') the subjectmust lean forward directing the body weight vector F_(BW) rearward as inFIG. 7c. FIG. 3b shows resultant unbalanced forces in that X₂ is largerthan X₁ and thus produces a net horizontal force in the X₂ direction.Vectors can be altered by cables 170 and 171 to produce such a neteffective force in either of two ways. Their tension can be relativelyaltered, that is, tension can be increased in the rear cable 171 orsubject can equal cable tension by the automatic process of leaningforward. Alternatively cable 170 can be shortened increasing angle θwhile reversing the process in the rear cable. In either case, thedifference in horizontal vectors is detected by running the subjectforce cables 212 and 211 over frictionless pulleys 213 and 214, shown inFIG. 6. Each pulley is supported by force sensitive elements 215 and 216in which electrical signals are developed. The desired value resultsfrom the rear signal F_(X2) measured by element 216 subtracted by thatof the front signal F_(Z1) measured by element 215. This is done asfollows.

A pair of horizontal strain gauges 215 and 216 sensitive only in thehorizontal X-axis are used. Such gauges are well known and commerciallyavailable. Gauges manufactured by Omega Inc. of Stanford, Connecticutare used in the preferred embodiment of the invention. The total meanhorizontal force F_(x) is obtained by subtracting and averaging 217 theoutput forces measured by the two gauges 215 and 216, which removes thestatic tension component. This can be done by direct connection of thegauges 231 and 232, or 234 and 235 as shown in FIGS. 8a and 8brespectively, or with summing amplifiers 239, 240, and 241 and resistors242, 243, and 244 as shown in FIG. 8c. The values for the operationalamplifiers 233 and 236 shown in FIGS. 8a and 8b as well as the resistorsand operational amplifiers shown in FIG. 8c can easily be determined byone skilled in the art. The configuration in FIG. 8a is one currentlyused in the preferred embodiment. The output of the subtracting orsumming function is fed into an averaging network such as the one shownin FIG. 5c to produce a total mean horizontal force, F_(x). Once thisvalue is known and oriented to the treadmill reference F_(X'), thetreadmill grade may be simply calculated by known electronic techniquesfrom the relationship F_(X') /F_(BW) where F_(BW) is derived from##EQU1## as by block 218 in FIG. 6.

Thus, with a passive treadmill and the instrumentation shown in FIG. 6,body weight 219, grade 219, and mode 204 can be derived.

CORRECTION FEATURE

The above relationships are valid only if the subject does not introduceother forces such as those associated with holding on to a handle. Insuch a case, these forces must be accounted for by techniques used andshown in FIGS. 9a and 9b.

A handle 245 is supported by structural members 246 through forcesensitive elements, generally referred to as 247, which respond only tohorizontal 248 and vertical forces 249.

Force signals resulting from pressure on handle 245 that are componentsof F_(x') and F_(Z') may be processed as described earlier andappropriately added to horizontal forces F_(Z') and vertical forcesF_(Z') resulting on the treads to correct any errors which might derivefrom extraneous support other than that from the tread itself.

TREAD VELOCITY MEASUREMENT AND CONTROL

To make treadmill work in weightlessness equivalent to that on Earth,tread velocity must be known and controlled. Measurement of velocity iscurrently done on United States treadmills with conventional electrictachometer and display. A wide range of such devices are available. Inthe preferred embodiment of this invention shown in FIG. 6, tachometer221 measures velocity of tread 204. This value is then displayed 222.

It is also desirable to control speed and this is currently done in theUnited States program by a brake which rapidly increases friction abovea range of any desired adjustable limit. The subject increases speeduntil increased force is sensed and runs just below that limit. Thesubject thus becomes a part of a sensitive and accurate speed controlservo loop. A more extensive control is described under the motor drivefor angle control.

With the above apparatus, passive treadmills can be instrumented toprovide the same information commonly used on Earth as well asadditional information, i.e., F_(Z) component of foot ground force.

WORK MEASUREMENT AND CONTROL

Testing and training techniques using treadmills adapted forweightlessness can be employed using familiar procedures and quantitiessince Earth body weight can be accurately simulated. Once this is done,familiar standards based on velocity and grade can be used to establishconventional work loads.

Should external or treadmill loads be desired, this can be simply anddirectly derived by analog or digital multiplication of the meanhorizontal force on the tread F_(x) and the velocity V_(TM) of the treadto obtain the value in absolute terms as shown in the followingequation:

    F.sub.x · V.sub.TM = Work[External]

AUTOMATIC GRADE/SPEED CONTROL

Passive treadmills require a minimum grade to operate. This may beovercome and the grade made continuously variable by an alternateembodiment of this invention shown in FIGS. 10 and 11. An alternativespeed control is also provided by this technique.

Apparatus shown in FIG. 11 provides a means for measuring andmaintaining a predetermined Earth equivalent grade and consequently awork rate applied to an active motor controlled treadmill by a userthereof. The theory behind this embodiment is that the system willcompare actual measured forces with calculated desired forces todetermine whether the resultant speed and grade which determine workrate are achieved. If not, the system will make automatic adjustments toforce the user to perform at the desired grade and velocity, hence thetotal work rate.

Referring to FIG. 10, a method of measuring and maintaining apredetermined work rate is shown. First, a user selects a speed andgrade angle associated with the predetermined work rate, step 250. Thenthe actual vertical force of the user, the equivalent body weight, ismeasured, displayed, and adjusted as necessary as previously describedin step 251. The force remains constant for a given subject performingat a given mode of locomotion and velocity.

Once the actual vertical force is measured, an equivalent vertical forceassociated with the selected grade angle is generated, step 252. Fromthis equivalent vertical force, an equivalent horizontal forceassociated with the selected grade is generated, step 253, and comparedto an actual measured horizontal force, step 254, produced by the userto generate an equivalent grade angle motor control signal, step 255.The motor is adjusted automatically in accordance with this controlsignal, step 257.

The actual velocity of the tread is measured, step 254, and compared tothe selected velocity, step 256, to generate a velocity control signal.The motor is also adjusted automatically in accordance with the velocitycontrol signal, step 257. The exact order of the horizontal forcecomparisons and velocity comparisons is not critical.

Referring now to FIG. 11, where an apparatus implementing this method isshown, this mode of operation is done by first specifying an equivalentgrade angle θ_(ref) and reference velocity V_(ref) associated with adesired work rate.

The total mean vertical force F_(zref) on the subject 260 is thenmeasured, by the means described earlier, and stored or alternatively,continuously measured by an apparatus shown in FIG. 6. A horizontalforce component reference signal F_(xref) generated by correcting thetotal mean vertical force F_(zref) signal for the desired grade angleθ_(ref) by a variable resistance 261, which varies with cos θ_(ref) inaccordance with the equation, F_(zadjusted) = F_(zref) · Cos θ_(ref).Variable resistors presently available on the market can easily beselected and used by someone skilled in the art. This procedure isconsistent with the description of calculating forces from the forcediagram described earlier, as shown in FIGS. 7a, 7b and 7c.

The adjusted reference voltage F_(yadjusted) is sent through a buffer262 and divided by a ganged resistor 263, which produces the referencedhorizontal voltage F_(xref) to satisfy the equation, F_(xref) =F_(yadjusted) · Tan θ_(ref). This voltage is passed through buffer 264and is applied to a high gain error amplifier 265, which comparesreferenced horizontal voltage F_(xref) actual measured horizontal forceF_(x). The actual horizontal force is measured in the same manner asdescribed in a previously described embodiment. The error or correctionvoltage is converted by a voltage to current device 266 to current inseries with the motor 267. Motor 267 and tachometer 268 are mechanicallycoupled to the treadmill 269. Motor torque, which is a function of thecurrent, will be limited to the maximum available current determined bythe error signal from the high gain amplifier 265. The referencevelocity signal, V_(ref), is provided for comparison to the actual speedsignal measured by tachometer 268 at buffer 27.

A high efficiency, permanent magnet servo motor is used in thisembodiment because of its very low inertia characteristic and rapidresponse plus desirable response to voltage and current.

Operation of this embodiment is as follows: with desired speed V_(ref)and angle θ_(ref) selected and the treadmill quiescent, the subject 260pushes the belt of the treadmill and generates a large force F_(x)signal to allow motor current to flow and motor torque to aid thesubject bringing the treadmill to its limit speed determined by V_(ref).If this speed is reached and exactly maintained, the amount of forceF_(x) required is equal to the F_(xref). To maintain this condition, thesubject or user must produce a force F_(x). If such user exceeds thislevel, the force-current loop of strain gauge 271, amplifier 265,voltage-to-current converter 266, and motor 267 will increase thetorque. Reduction of torque is accomplished by a reverse procedure. Thesubject must consciously attempt to increase speed to the preset limit,V_(ref). When this limit is reached, the velocity control loop of motor267, amplifier 270, and tachometer 268 reduces motor drive voltage. Byadding a reverse current diode 272, unlimited current may be used to notonly absorb power or in the case of significant error to produce areverse torque.

Also note that while hands-off operations are the desired norm inweightlessness, if the subject handrail is used, force sensing aspreviously described will be used to detect net horizontal forces F_(x),which are then summed with those detected by the subject weightequivalent force system.

The preferred embodiments just described are specifically designed toovercome the problems associated with the weightless environment inspace. However, such apparatus is perfectly capable for use on Earth.

MANUAL GRADE/SPEED CONTROL

A simple manually operated driver motor could easily be attached to thepassive system shown in FIG. 6 by one skilled in the art. A user turnsthe motor on and adjusts it to reach a desired grade or treadmillvelocity. Once a desired level is obtained, the motor is set to maintainthe grade and or speed.

While particular embodiments of the invention have been shown anddescribed, it will be understood that the invention is not limitedthereto, since many modifications may be made and will become apparentto those skilled in the art.

I claim:
 1. Method of quantifying the subject work rate in a weightlessenvironment in terms of an equivalent grade factor, the internal workrate, and external work rate, applied to a treadmill over a period oftime by a user thereof, which comprises the steps ofmeasuring at aplurality of locations along the treadmill total instantaneous verticalforces applied by the user when in a mode of motion, averaging saidtotal instantaneous vertical forces over time to develop an averagevertical force which is equal to an equivalent body weight, measuringalong the treadmill relative to the user instantaneous horizontal forcesapplied by the user when in motion, averaging said instantaneoushorizontal forces over time to produce an average horizontal force,measuring velocity of the treadmill, deriving from said equivalent bodyweight, said velocity of the treadmill, and said mode a measure ofinternal work rate, multiplying said average horizontal force by saidvelocity of the treadmill to produce a measure of the external workrate, deriving the equivalent grade factor of the treadmill from saidaverage vertical force and said average horizontal force, and applyingto the user an adjustable vertical force to produce a predetermineddownwardly directed vertical force on the treadmill.
 2. Method inaccordance with claim 1, wherein said step of applying an adjustablevertical force comprises the step ofattaching adjustable essentiallyconstant force generators from the user to another surface.
 3. Apparatusfor quantifying the subject work rate applied to an exercise device by auser and adapted for use in a weightless environment, comprisingatreadmill, means for applying to the user an adjustable vertical forceto produce a predetermined downwardly directed vertical force on thetreadmill, a plurality of vertical strain elements connected evenlyspaced along the treadmill, each vertical strain elements beingsensitive only to vertical force to produce a resulting electricalsignal, averaging means connected to said vertical strain elements forproducing an average vertical signal over time, horizontal strainelement means connected to the treadmill relative to the user sensitiveto measure only horizontal force and to produce a resulting electricalsignal, averaging means connected to said horizontal strain elements forproducing an average horizontal signal over time, a tachometer connectedto the treadmill for producing a speed signal equal to the velocity ofthe treadmill, a means for deriving an internal work rate signal fromsaid average vertical signal, said speed signal, and mode of locomotion,and a multiplier network connected to produce the product of saidaverage horizontal signal, and speed signal, said multiplier networkproduct being an external work rate signal.
 4. Apparatus in accordancewith claim 3, wherein means for applying an adjustable vertical forcemeans includes bungee cords attached from the user to another locationon same plane as and relative to the treadmill.
 5. Apparatus inaccordance with claim 3, and including a braking means for limitingmaximum velocity of the treadmill.
 6. Method of quantifying externalwork rate in a weightless environment applied to a treadmill by a userthereof, which comprises the steps ofmeasuring along the treadmillrelative to the user instantaneous horizontal forces applied by the userwhen in motion, averaging said instantaneous horizontal forces over timeto produce an average horizontal force, measuring velocity of thetreadmill, multiplying said average horizontal force by said velocity ofthe treadmill to produce a measure of the external work rate, andapplying to the user an adjustable vertical force to produce apredetermined downwardly directed vertical force on the treadmill. 7.Apparatus for quantifying the external work rate applied to an exercisedevice by a user and adapted for use in a weightless environment hereof,comprisinga treadmill, means for applying to the user an adjustablevertical force to produce a predetermined downwardly directed verticalforce on the treadmill, horizontal strain element means connected to thetreadmill relative to the user sensitive to measure only horizontalforce and to produce a resulting electrical signal, an averaging meansconnected to said horizontal strain element for developing an averagehorizontal force, a tachometer connected to the treadmill for producinga speed signal equal to the velocity of the treadmill, and a multipliernetwork connected to produce a product of said average horizontal signaland said speed signal, said multiplier network product being a measureof the external work rate.
 8. Apparatus in accordance with claim 7, andincluding a braking means for limiting the maximum velocity of thetreadmill.
 9. Method of quantifying the internal work rate in aweightless environment applied to a treadmill by a user thereof, whichcomprisesmeasuring at a plurality of locations along the treadmillinstantaneous vertical forces applied by the user when in a mode ofmotion, averaging said instantaneous vertical forces to develop anaverage vertical force equal to an equivalent body weight, measuringvelocity of the treadmill, deriving from said equivalent body weight,said velocity of the treadmill, and said mode a measure of the internalwork rate, and applying to the user an adjustable vertical force toproduce a predetermined downwardly directed vertical force on thetreadmill.
 10. Apparatus for quantifying the internal work rate appliedto an exercise device by a user and adapted for use in a weightlessenvironment thereof while in a mode of locomotion, comprisingatreadmill, means for applying to the user an adjustable vertical forceto produce a predetermined downwardly directed vertical force on thetreadmill, a plurality of vertical strain elements connected evenlyspaced along the treadmill, each vertical strain element being sensitiveonly to vertical force to produce a resulting electrical signal,averaging means connected to said vertical strain elements for producingan average vertical signal, a tachometer connected to the treadmill forproducing a speed signal equal to the velocity of the treadmill, and ameans for deriving the internal work rate from said average verticalsignal, said speed signal, and the mode of locomotion.
 11. Apparatus inaccordance with claim 10, and including a braking means for limitingmaximum velocity of the treadmill.